Farmhouse Straub

87527

Sonthofen, Germany

Architect

Michael Felkner
Niedersonthofener Straße 8, 87448 Waltenhofen-Oberdorf

Contact Details

Katrin Hippeli, Simon Fiedler
Hochschule Coburg
Simon.Fiedler@stud.hs-coburg
Julia Greulich
Authentic, energy-efficient and ecological: the Straub family had specifically looked for an old farm; together with the architect, they succeeded in creating a cosy home. For the most part, the traditional use was retained, in some places reinterpreted for today's requirements. The historic building fabric from the 18th century was in good condition and was preserved as well as staged with modern materials. This also succeeds under the premise of sustainability, through insulation with cellulose fibres as well as a pellet boiler and solar panels for heating and hot water.
Energy performance
47,3 kWh/m2.y

Climate Zone transition region between marine and continental climate

Altitude 890

HDD 4398

CDD 0

Protection level Not listed

Conservation Area:
No

Level of Protection:

Building age 1700-1800

Year of last renovation:
2018

Year of previous renovation:
0

Building use Residential (rural)

Secondary use:
NA

Building occupancy:
Permanently occupied

Number of occupants/users:
10

Building area Net floor area [m²]: 568,1

Building typology:
Detached house

Number of floors:
2

Basement yes/no:
Da

Number of heated floors:
2

Gross floor area [m²]:
664,91

Thermal envelope area [m²]:
831,1

Volume [m³]:
1404,6

NFA calculation method:
NGF (de)

Construction type
Solid timber wall

External finish:
Exposed woodwork

Internal finish:
Exposed woodwork

Roof type:
Pitched roof

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Julia Greulich
Julia Greulich
Julia Greulich
Julia Greulich
Julia Greulich
Julia Greulich
Julia Greulich
Julia Greulich
Julia Greulich
Julia Greulich
Julia Greulich
Julia Greulich
Julia Greulich
Julia Greulich
Julia Greulich
Julia Greulich
Michael Felkner
Michael Felkner
Michael Felkner
Michael Felkner
Michael Felkner
Michael Felkner
Michael Felkner
Michael Felkner
Michael Felkner
Michael Felkner
Michael Felkner
Michael Felkner
Michael Felkner
Michael Felkner
Michael Felkner
Michael Felkner
Julia Greulich
Julia Greulich
Julia Greulich
Julia Greulich
Julia Greulich
Julia Greulich
Julia Greulich
Julia Greulich
Michael Felkner
Michael Felkner
Michael Felkner
Michael Felkner
Michael Felkner
Michael Felkner

RENOVATION PROCESS

Architecture

BUILDING DESCRIPTION

From the roof construction, the building was probably built in the 18th century. The farmstead with the kitchen, parlour and loft is knitted (built in block construction) and stands on a basement built into the slope, with the wide and not very high windows typical of weaving cellars. On the eastern gable end adjoins the barn and threshing floor, a timber-framed structure with boarding, and over both parts of the building stretches the all-unifying flat pitched gable roof, a so-called Allgäu flat roof. The block walls were partly plastered and partly panelled on the inside. The gable triangle, the longitudinal barn and the threshing floor have always been vertically boarded. The exterior plastering of the farmstead, made of coarse pointed plaster, probably dates from later times; it is possible that the house floor was originally openly visible or shingled, as is typical for the region.
Urban context
The farmhouse is located in a small scattered village named Imberg. On the northern eaves line there is the access from the road. To the southeast you have a free view over the slope.

HERITAGE SIGNIFICANCE

ELEMENTS WORTHY OF PRESERVATION
Some windows, like between the kitchen and the loggia in the second floor, have been kept and new windows were added inside. The main door in the first floor, which is now used in the basement, as well as the wall and ceiling paneling were considered to be of historical value, too.
Heritage Value Assesment
The building is not listed. However, the well done historical construction and the numerous well preserved elements typical for the region led to owner, but also the funding agency KfW consider it "worthy of preservation"..

State of repair

Conditions of the envelope
Most of the constructive elements were in good condition. However, due to inappropriate interventions, the eastern gable wall suffered from distortion. On the western side the wooden railing rotted. Also the southern basement wall was in dangerous state and the footings were not intact. Because of the humid ground the timber walls in the basement rotted, too.
Description of pre-intervention building services
Except of two ovens in the kitchen and the parlour there were no heat sources. The sanitation was limited to a washing opportunity in the laundry and a privy.

Aim of retrofit

Renovation
The building was to be comfortably habitable and, after a renovation that preserved its historical values, meet current energy and age-related requirements - for the owner's family and two additional flats. The substance of the log building was clearly suitable for renovation, and the barn was also too well preserved to simply demolish it - the beautiful log walls and handcrafted roof structure rather awakened the desire to create an interesting field of tension between tradition and modernity. The design and refurbishment concept therefore make strong use of the existing structures: The log building is staged as an atmospheric element on the inside and insulated and shingled on the outside for this purpose. In the area of the former barn, the construction is preserved and visible from the inside by placing prefabricated timber frame walls in front of it - the vertical battens still preserve the character, and new large windows bring light into the rooms. The exposed roof truss offers the owners a special spatial experience in their new home, which is further emphasised by rooms that stand inside as boxes. The longitudinal barn on the south side becomes a semi-open space, a veranda in summer, and can be used almost all year round thanks to the folding and sliding windows.
Was there any change of use?
Now the adjoining barn has also a residential use.
Lessons learned
During the building process there were historical ceilings and other elements discovered.
Stakeholders Involvement
Architect
Michael Felkner
Niedersonthofener Straße 8, 87448 Waltenhofen-Oberdorf
Tools used
Was the renovation process done following a specific methodology? No

RETROFIT SOLUTIONS

External Walls

Log wall, exterior insulation

Log wall, interior insulation

barnwall

Log wall, exterior insulation

The block construction of the farmstead is thermally insulated on the outside: a total of 24 cm of cellulose insulation is blown in between the battened construction timber. A 6 cm thick latex-impregnated wood fibre board, which could also have been plastered, but in this case was shingled, forms the finish.

The choice of materials for the interior plaster (clay plaster), the insulation (cellulose insulation and wood fibre boards) and the façade (wooden shingles) is very sustainable, adapts to the existing building and guarantees an extended lifespan of the existing wall.

U-value (post-intervention) [W/m2K]: 0,13 W/m²K
More Details
Original wall build-up
Render - Partly rendered:
15 mm
Wood - Wall of log-construction, spruce:
140 mm
Render - Render:
20 mm
Retrofitted wall build-up
Render - Clayrender:
30mm
Wood - Wall of log-construction, spruce:
140 mm
Insulation - Cellulose-Insulation/Timber-frame:
240 mm
Insulation - Grain, insulating wall panel:
60 mm
Log wall, interior insulation

The block wall to the veranda is insulated on the inside with 20 cm wood fibre board and also finished with clay plaster.

This way it is possible to keep the historic materials visible. The veranda are located where once there were the laundry and privy.

U-value (post-intervention) [W/m2K]: 0,16 W/m²K
More Details
Original wall build-up
Render - Partly rendered:
15 mm
Wood - Wall of log-construction, spruce:
160 mm
Retrofitted wall build-up
Render - Clayrender:
30mm
Insulation - Grain insulation:
200 mm
Wood - Wall of log-construction, spruce:
160 mm
barnwall

Additional timber framed wall in front of the existing beams with 28 cm cellulose insulation and 6 cm wood fibre insulation boards on both sides. The inner wood fibre board also serves as an installation layer, the adjoining OSB board as a vapour barrier. Towards the rooms, the new construction is mostly plastered, outside again with vertical wooden boarding.

The historical bolt work and the special roof structure are kept visible on the inside. They are protected from weather conditions and cold by the timber-framed wall in front of it.

U-value (pre-intervention) [W/m2K]: 0,0 W/m²K U-value (post-intervention) [W/m2K]: 0,11 W/m²K
More Details
Original wall build-up
Wood - bearing timber construction:
200 mm
Wood - timber cladding:
20 mm
Retrofitted wall build-up
Render - Clayrender:
30mm
Insulation - Layer of installation: Grain insulation and timber battens:
60 mm
Wood panelling - Oriented strand board:
15 mm
Insulation - Cellulose-Insulation/Timber-frame:
280 mm
Insulation - Grain, insulating wall panel:
60 mm


Windows

Window in the barn

Window in the farmhouse, first floor box-type window north side

Window in the farmhouse

Preserved original windows

Window in the barn

New window with triple glasing

no existing window before at this spot

Existing window U-value Glass [W/m2K]: 0,0 New window U-value Glass[W/m2K]: 0,5 Existing window U-value Frame [W/m2K]: 0,0 New window U-value Frame [W/m2K]: 1,15
More Details
Existing window type no existing window before at this spot
Existing glazing type no existing window before at this spot
Existing shading type NA
New window type Sliding window
New glazing type Triple
New shading type NA
New window solar factor g [-] 0,53
Window in the farmhouse, first floor box-type window north side

New window with triple glasing

The box-type windows were replaced by wooden double windows with glazing bars. Their design is inspired by the historical window division.

Existing window U-value Glass [W/m2K]: 2,73 New window U-value Glass[W/m2K]: 0,5 Existing window U-value Frame [W/m2K]: 0,79 New window U-value Frame [W/m2K]: 1,15
More Details
Existing window type Box-type window
Existing glazing type Single
Existing shading type Outer shutter
Approximate installation year 1940
New window type Double window
New glazing type Triple
New shading type Outer shutter
New window solar factor g [-] 0,53
Window in the farmhouse

New window with triple glasing

In general, the historical windows have specific divisions of glazing bars depending on their direction. The design of every new window in the farmhouse is inspired by the historical window division of the northern facade. The windows were replaced by wooden double windows with glazing bars.

Existing window U-value Glass [W/m2K]: 5,67 New window U-value Glass[W/m2K]: 0,5 Existing window U-value Frame [W/m2K]: 1,58 New window U-value Frame [W/m2K]: 1,15
More Details
Existing window type Double window
Existing glazing type Single
Existing shading type Outer shutter
Approximate installation year 1900
New window type Double window
New glazing type Triple
New shading type Outer shutter
New window solar factor g [-] 0,53
Preserved original windows

In some areas, the original windows were retained: In the loggia, for example, where an improvement of the thermal properties was not necessary.

The original windows in the gable on the west wall were also repaired and preserved and an additional window level was added on the inside

Existing window U-value Glass [W/m2K]: 5,7 Existing window U-value Frame [W/m2K]: 2,1
More Details
Existing window type Sash window
Existing glazing type Single
Existing shading type NA
New window type

Other interventions

ROOF

GROUND FLOOR

OTHER

MEASURES TO INCREASE AIRTIGHTNESS

ROOF

The existing roof truss was kept and new rafters and insulation were installed.

The shape and the structure of the roof were kept and because of the removed ceiling it is now visible from the living room underneath. The rafters were mostly replaced and can also be seen from the inside due to the exterior insulation.

U-value (pre-intervention) [W/m2K] 3,5 U-value (post-intervention) [W/m2K] 0,14
More Details
Original roof build-up
Tiles - Rooftiles:
20 mm
Other - Battens:
30 mm
Other - Rafters:
140 mm
Retrofitted roof build-up
Metal sheets - Metal sheet:
2 mm
Other - Grain, insulating roof panel:
60 mm
Other - Cellulose insulation/timber battens:
280 mm
Other - Spruce cladding:
15 mm
GROUND FLOOR

Due to the low clear hight of the first floor and the basement, the bottom and the ceiling of the basement were lowered. The ceiling of the basement got an insulation.

Because of the more appropriate clear hight the first floor complies with modern demands. Therefore this huge intervention is absolutly justifyable.

U-value (pre-intervention) [W/m2K] 1,2 U-value (post-intervention) [W/m2K] 0,18
More Details
Original groundfloor build-up
Floor joists - Wooden ceiling joists:
180 mm
Other - Wooden planks:
40 mm
Retrofitted groundfloor build-up
Other - Spruce:
24 mm
Insulation - Cellulose insulation / Ceiling joist:
200 mm
Other - Oriented strand board:
20 mm
Insulation - Floor impact protection:
30 mm
Other - Spruce:
20 mm
OTHER

At the south side the barn was transformed into loggias for entering the apartments and relaxing.

The nowadays unnecessary farming use was replaced by an outside relaxing area inside the loggias including an open staircase. Since that there is an additional value for this space and the main entrance was kept at the south side of the building.

MEASURES TO INCREASE AIRTIGHTNESS

No blower door test was carried out (yet), but an airtightness concept was drawn up in the planning phase, which was also carried out accurately - not least due to the constant presence of the architect, especially in the final phase of the interior construction. Since not all areas are plastered, the airtight layer does not follow the internal plaster, as is often the case, but essentially the vapour retarders - in the roof and in most of the external walls - which were connected well to each other. The transition from the externally insulated area of the block wall to the internally insulated area (facing the veranda) remains the weakest point.

HVAC

HEATING

DOMESTIC HOT WATER

HEATING

The existing ovens moved from the first floor to the second floor, but they are not the main heat source anymore. The demanded heat is now generated by a pellet boiler and a solar heating system.

The fact that the historic stoves have been preserved and continue to be used lends authenticity to the entire building. Thanks to the use of biomass, the building also performs very well in terms of primary energy: of the heating requirement for space heating of 13,350 kWh (see balance sheet as graph and table), which results in a final energy requirement of 15,464 kWh including losses and auxiliary energy, only 4,200 kWh of primary energy requirement remain - this corresponds to 7.4 kWh/m².

More Details
New primary heating system New secondary heating system
New system type Stove NA
Fuel Biomass Solar energy
Distribuition system Radiating wall Radiating wall
Nominal power 18,0 kW kW
DOMESTIC HOT WATER

Hot water is produced by the solar system in summer, which is supported by the pellet boiler in winter. In a renovated building like this, domestic hot water accounts for a good third of the final energy demand.

Since the flat pitched roof the solar modules can not be seen from the surroundings.

More Details
New DHW system
Type with heating system
Hot_water_tank Da
With heat recovery No

RENEWABLE ENERGY SYSTEMS

SolarThermal

Photovoltaic

SolarThermal

During the renovation a solar energy plant was installed on the rooftop, which supports the domestic hot water production.

Since the flat pitched roof the solar modules can not be seen from the surroundings, so the appearance is not disturbed. Besides that the solar energy plant reduces the demand of primary energy, so the building can be used more sustainable.

More Details
SolarThermal System
Type Flat collector
Collector area 12,0 m²
Elevation angle 15,0
Azimuth 0,0
Overall yearly production 3106,09 kWh
Heating_contribuition 0,0 kWh
DHW contribuition 3106,09 kWh
Cooling contribuition 0,0 kWh
Photovoltaic

During the renovation a photovoltaic system was installed on the rooftop, which produces electricity.

As well as the solar energy plants the pv-modules can not be seen from the surroundings, so the appearance is not disturbed. Besides that the pv-modules reduces the demand of primary energy, so the building can be used more sustainable.

More Details
Photovoltaic System
Type NA
Collector area
Elevation angle 15,0
Heating contribuition 0,0 kW
DHW contribuition 0,0 kW
Cooling contribuition 0,0 kW

Energy Efficiency

Energy Performance
Energy performance certificate: The building has an energy performance certificate with a primary energy demand of 12,3 kWh/(m²a) from June, 30th 2020. (Final energy demand: 47,3 kWh/(m²a))
Voluntary certificates: KfW-Effizienzhaus 55
Energy Use
Heating
Consumption_estimation_Calculation_method: Steady state simulation (e.g. EPC, PHPP)
Consumption_estimation_After: 47,3 kWh/m2.y

Primary Energy
Consumption_estimation_Calculation_method: Steady state simulation (e.g. EPC, PHPP)
Documents:
200630_GEA.pdf
Consumption_estimation_Including_DHW: Da
Consumption_estimation_After: 12,3 kWh/m2.y

Internal Climate

Temperature

The demanded temperature for the inside is 20 ° C.

Indoor Air Quality

The indoor quality is fine.

Daylight

The position and sizes of the existing windows in the farmhouse have not been altered, so there is no change in lightning. On the other hand the new windows in the barn have modern sizes, so the rooms behind them seem bright and friendly.

Acoustic Comfort

The acoustic comfort is fine.

Artifact Conservation

NA

Costs

Financial Aspects

The cost breakdown of 930'000,-€ includes both the energetic renovation (with 530'000,-€) and the adaptation to age-appropriate living (with 400'000,-€), including VAT of 19%. The following subsidies could be used: 1.)Subsidy from the KfW programme "Energy-efficient renovation": 3x120'000,- at 0.75% interest, 10 years fixed interest and 144'000,- repayment subsidy (thanks to reaching KfW Efficiency House 55. 2.)Subsidy from KfW's "Altersgerecht Umbauen" programme: 3x50,000 at 0.75% interest, 10 years fixed interest. 3.) Bafa heating subsidy: approx. 20'000,-€ investment subsidy 4.) KfW Building Assistance Programme 4'000,- € subsidy 5.) District programme construction support 4'000,-€ subsidy. So, in addition to the favourable interest rate, approx. 172'000,-€ came from the state.

Investment Costs
Total investment costs
1640,- € (per m2)
Amount includes: The cost breakdown of 930'000,-€ includes both the energetic renovation (with 530'000,-€) and the adaptation to age-appropriate living (with 400'000,-€), including VAT of 19%.

Cost of energy related interventions:
930,-€ (per m2)
Amount includes: This value includes not only the additional costs for the energy-efficient refurbishment, but also all the investments in connection with the energy-efficient refurbishment, i.e. also all the repairs and maintenance measures that are necessary anyway.
Running Costs
Lifecycle cost
No

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